Visualisation of Tissue and Cells - Week 6 Flashcards
Explain why light refracts when passing through a lens
its due to the the higher optical density of glass compared to air- (it travels slower through glass lens in comparison to air)
Explain how wavelength of radiation and numerical aperture affect resolution (give equation and explain it)
resolution distance= 0.61 x wavelength/ numerical aperture
*the higher number that the numerical aperture is the lower resolution- can see more in detail
*resolution distance is directly dependent of wavelength but indirectly dependent on numerical aperture
what is it meant by numerical aperture
its the ability of an object to collect light
Compare the structure of the light microscope with the structure of the electron microscope
-wavelength of light= 400-700nm, wavelength of electron micro=0.01-0.001nm
-light micro gives coloured image electron micro doesn’t
-can be used with live unstained cells & fixed stained specimens where as electron micro can only work with fixed stained specimens
-electron uses electron beams, & light micro uses beam of light
describe the light path through a light microscope in order
line of vision- ocular lens- prism- objective lens- specimen- condenser lens- illuminator
what is the purpose of immersion oil
increase resolution as it doesn’t allow light to bend as the oil has the same optical density as the glass and basically is able to collect the light
equation for the total magnification of the light microscope
magnification of objective lens x magnification of ocular lens
what are the steps for preparing specimens for microscopy (4 steps)
1) Fixation of tissue
2) Embedding in a supporting medium
3) Sectioning into thin (transparent) sections
4) Staining sections to enhance contrast
what are the 2 ways of fixation in the fist step of preparing specimens for microscopy
- Chemical Fixation: use of cross-linking chemicals & Dehydration reagents( e.g. ethanol)
-Physical Fixation: freezing at -70 degrees
